Gastrointestinal (GI) neuromuscular disorders (motility disorders) are characterized by dysfunctions of three types of key cells: interstitial cels of Cajal (ICC), enteric nervous system (ENS), and smooth muscle cells (SMCs), which cooperatively control SM motility in the GI tract. ENS and ICC generate complex rhythmic motor behavior and spontaneous electrical slow waves, respectively, both of which control SMCs, the final effectors for muscle contraction and muscle relaxation. Although there has been a significant amount of work investigating the effects of ENS and ICC dysfunction in GI motility disorders, the dysfunction of SMCs has received much less attention. The gap in the knowledge of SMC dysfunction needs to be addressed, since the three types of cells are physically associated and functionally working together: dysfunction of one cell type can affect the other two. This present project seeks to uncover a molecular mechanism for understanding how SMCs are remodeled during the development of GI motility disorders. We have recently reported that GI SMCs require microRNAs (miRNAs) for the development and survival of animals, and that the phenotypes of GI SMCs are controlled by serum response factor (SRF)-dependent microRNAs. In addition, our preliminary study suggested that the phenotypic change (hypertrophy) of SMCs is linked to dysregulation of a unique set of SRF-dependent miRNAs which are regulated by epigenetic DNA methylation. To study this new molecular mechanism, we generated six transgenic animal models that display abnormal phenotypes of SMCs during the embryonic and post-natal development of the cells. In this project, we propose three specific aims: define the roles of SRF-dependent miRNAs during the development of GI SMCs, define the roles of DNA methylation during the development of GI SMCs, and discover the roles of DNA methyltransfertase (Dnmt1)-targeting miRNAs that regulate GI SMC hypertrophy. Completion of the specific aims of this project will provide an exciting new mechanism for understanding how the SRF-dependent miRNA genes are epigenetically reprogrammed in the SMCs of GI neuromuscular disorders. Identifying the epigenetic changes will aid not only in the development of a diagnostic tool for hypertrophy-related diseases, but also of a therapeutic target that has the potential to reverse the epigenetic changes that are responsible for these pathological conditions, and thus possibly reverse some of the unwanted pathological changes that occur in these disorders.